1. Field of the invention
The invention relates in general to a display panel and in particular to a liquid crystal display (LCD) panel.
2. Description of Related Art
The conventional LCD panel is formed by a color filter substrate, a thin film transistor (TFT) array substrate, and a liquid crystal layer sandwiched therebetween. Recently, techniques of directly forming color filter on array (COA) and forming black matrix on array (BOA) have been proposed. Specifically, a COA substrate or a BOA substrate is assembled to an opposite substrate, and liquid crystal molecules are then trapped between the two substrates to constitute an LCD panel.
In general, the liquid crystal molecules can be introduced between the two substrates by way of vacuum suction or one drop fill (ODF). Since the dimension of the LCD panel increases, it is rather time-consuming to introduce the liquid crystal molecules between the two substrates by vacuum suction. Hence, in an assembly process of a large-size LCD panel, the liquid crystal molecules are introduced between the two substrates by way of ODF in most cases. In particular, prior to the ODF, a sealant is formed at boundaries of a display area of an active device array substrate, so as to define liquid crystal accommodation space. The amount of the dropped liquid crystal molecules is determined based on the dimension of the liquid crystal accommodation space and a cell gap between the two substrates, such that the liquid crystal molecules with certain volume are dropped into the liquid crystal accommodation space. The active device array substrate and the color filter substrate are then aligned and assembled, and the sealant is cured to trap the liquid crystal molecules between the two substrates.
Nevertheless, when the liquid crystal molecules are introduced between the two substrates by way of ODF, the liquid crystal molecules are diffused to the periphery of the sealant in a capillary manner. In the LCD panel having the COA substrate or the BOA substrate, vias between pixel electrodes and drain electrodes of active devices cannot be fully filled with the liquid crystal molecules when the liquid crystal molecules are diffused to the periphery of the sealant due to the insufficient capillary force. Thereby, vacuum bubbles are apt to be generated in the vias. The vacuum bubbles result in reduced yield of the LCD panel. Besides, the vacuum bubbles are located corresponding to the drain electrodes and the vias, and therefore the vacuum bubbles are not prone to be observed by naked eyes or image recognition systems. Accordingly, test balls have been developed to knock edge regions of the LCD (the periphery of the sealant), so as to further determine whether a bubble issue exists. However, even though the bubble issue can be detected by using the test balls, it is not likely to resolve the bubble issue effectively.